WASHINGTON (Reuters) - Scientists may have found a gene for fear -- a gene that controls production of a protein in the region of the brain linked with fearful responses.

Their finding, published on Thursday, could lead to new treatments for mental disorders such as post-traumatic stress disorder and generalized anxiety.

The gene, known as stathmin or oncoprotein 18, is highly concentrated in the amygdala, a region of the brain associated with fear and anxiety, the researchers report in Thursday's issue of the journal Cell.

"This is a major advance in the field of learning and memory that will allow for a better understanding of post- traumatic stress disorder, phobias, borderline personality disorder and other human anxiety diseases," said Gleb Shumyatsky of Rutgers University in New Jersey, who worked on the study.

"It will provide important information on how learned and innate fear is experienced and processed, and may point the way to apply new therapies."

Mice genetically engineered so they would not produce stathmin had brain irregularities and were less able to remember fear-conditioned responses, the researchers reported.

Learned fear develops after conditioning -- as when a person is stung by a wasp and fears the insects afterward. These memories are formed in the amygdala.

"This is the first time it has been shown that the protein called stathmin -- the product of the stathmin gene -- is linked to fear conditioning pathways," said Vadim Bolshakov, director of the Cellular Neurobiology Laboratory at Harvard University's McLean Hospital, who also worked on the study.

Also, the mice showed unusual behavior. Mice instinctively avoid open spaces, but the stathmin-free mice showed no fear and often explored more open areas than normal mice, the researchers found.

So the gene may control both learned and innate fear, the researchers said.

The mice might be useful for testing drugs and other treatments of anxiety disorders, they said.